Use of EFG technique to grow a Ga2O3 single crystal is known as a conventional method (see e.g., PTL 1). The method disclosed in PTL 1 in which a Ga2O3 single crystal is grown while gradually widening thereof from a contact portion with a seed crystal toward the bottom, i.e., while widening the shoulder allows obtainment of a flat plate-shaped crystal having a larger width than the seed crystal.